The world has witnessed a major wave of mergers and acquisitions (M&A) through the 1990s and up to 2007.A majority of these M&A deals are horizontal, involving the purchase of another company in the same industry. Such acquisitions imply a motivation to increase revenues by expanding market scope and/or market share, and/or by adding new products to the portfolio. They also suggest a pursuit of cost efficiencies in various aspects of operations. Whether these benefits are actually realised is an empirical question that has attractedresearch in several disciplines, including economics, finance and accounting. By now, there is a large body of research evidence to indicate that M&As have a poor record of success, with the main beneficiaries being the sellers who reap a one-off gain from the premium paid to acquire their firm.The objective of this dissertation was to examine post-merger performance from a marketing perspective, a topic that has not been explored thus far. This study followed a multi-stage approach; in the first stage an exploratory case study was conducted to identify the parameters of the research problem and to develop a set of hypotheses. Following this, a quantitative study of a sample of M&A transactions was carried out to test these hypotheses.The exploratory case study was based on Tata Motors, an Indian company which acquired Jaguar and Land Rover from Ford Motors. This case investigation based on both primary data collected through in-depth interview and a wide spectrum of secondary sources, showed that the acquisition had a significantly positive impact on Tata Motors' marketing performance, with sales volume and revenue growing significantly in the post-acquisition years. However, these sales increases came at a high cost; the company invested a huge amount in new product development and marketing communications, with the result that profit performance was negatively affected in the three years post-merger. Profit margins increased, however, in the seventh year 2014, suggesting that the reduction post-merger may have been a temporary effect.The quantitative study was based on a sample of forty-five M&A deals involving ninety US companies.This longitudinal study examined performance over six years, three before the merger, and three yearsafter the merger. Four analytical toolswere used:a paired sample t-test, an analysis of effect size, an analysis of covariance (ANCOVA), and regression analysis, to examine post-merger performance. The results of both raw data and log-transformeddata analyses showed that sales revenue increased significantlyin the post-merger years compared to the pre-merger years. Moreover, the combined companies reduced their marketing and selling costs in proportion to sales revenue. However, there was asignificant reduction in profit as measured by return on sales (ROS).Combining the findings from both the qualitative and quantitative studies, we concluded that post-merger marketing performance improved, i.e. sales revenue and cost of marketing and selling, but...